With the car on its wheels level lthe rocers front to rear. Align doors with out latches. Make sure whent they are in the closed position they align perfect. While they are in this position weld a brace from the top of the rear jam to the middle of the front . Do this on the inside so the doors still close.
leave the door in place while doing the rockers and the quarters and align them with the doors as a reference point.
These braces are an important step you don't want to skip. Never cut both quarters off at once unless you have another car there for references. Fit several times weld once.